Pulse Wave Measurement With In-Ear Headphones While Music Playback

Abstract

The continuous acquisition of the arterial pulse wave can be used to determine the heart rate and to estimate the blood pressure. Existing wearables require special sensors and often only detect the pulse wave at the extremities from the peripheral blood vessels, far away from the heart and aorta. In addition, these wearables are sometimes expensive and uncomfortable. The objective of this work is therefore the development of a comfortable wearable measurement system that continuously acquires the pulse wave. The approach presented in this work is based on the minor deformation of the ear canal when the pulse wave arrives. By sealing the ear canal using commercial headphones, these deformations are converted into small changes in air pressure. These pressure changes are detected directly by the headphones and converted into an electrical signal. An electronic measuring system was developed to record pulse waves and play music simultaneously. This system can be connected between any conventional audio source and headphones. The measuring system digitizes the low-frequency signal components and transmits them to an analysis system, such as a smartphone or PC. On this system, the signals undergo a digital signal processing chain. A subject measurement was conducted to evaluate the measurement approach. The music being played and an electrocardiogram were also recorded used as reference signals. The measurement demonstrated that with the new system, the pulse waves in both ears can be recorded during music playback with simple headphones and correlate with the electrocardiogram.